A link budget is an accounting of all of the gains and losses from a transmitter, through a medium (free space, cable, waveguide, fiber, etc.) to a receiver in a telecommunication system. It accounts for the attenuation of the transmitted signal due to propagation, as well as the antenna gains, feedline, and miscellaneous losses. Randomly varying channel gains such as fading are taken into account by adding some margin depending on the anticipated severity of its effects. The amount of margin required can be reduced by the use of mitigating techniques such as antenna diversity or frequency hopping.
An antenna's power gain or simply gain is a key performance number, which combines the antenna's directivity and electrical efficiency. As a transmitting antenna, the gain describes how well the antenna converts input power into radio waves headed in a specified direction. As a receiving antenna, the gain describes how well the antenna converts radio waves arriving from a specified direction into electrical power.
Guided media such as coaxial and twisted pair electrical cables, radio frequency waveguides, and optical fibers have losses that are exponential with distance. The path loss will be in terms of decibels (dB) per unit distance. This means that there can be a crossover distance beyond which the loss in a guided medium can exceed that of a line-of-sight path of the same length.
The above-described background relating to antenna and cable gains and losses are merely intended to provide a contextual overview of some current issues, and is not intended to be exhaustive. Other contextual information may become further apparent upon review of the following detailed description.